We are studying the evolution of structural gene families and of the regulatory elements controlling their developmental expression, using as a model system the silkmoth chorion multigene families. We have shown by protein characterization and sequence analysis, and by analysis of a cDNA clone library, that the major chorion proteins of silkmoths are encoded by families of evolutionarily homologous genes. We will continue to study how these genes evolve: by scattered or clustered substitutions, deletions/insertions (possible related to internal repeats), rearrangements (possibly related to sequence domains) or multiplication/loss of active genes leading to "coincidental evolution." We also want to study how genetic regulatory elements evolve: whether the temporal regulation of gene expression is very stable, as preliminary evidence suggests, whether the quantitative controls on expression (transcription and/or RNA processing) evolve rapidly, or whether the apparent changes in quantitative expression which we have observed are due to changes in gene multiplicity. These findings are to be related to the manner in which these multigene families are organized in chromosomal DNA. Finally, structure-function analysis of chorion proteins will be pursued as a long-term objective relevant to understanding their evolution.